Glare susceptibility tester

ABSTRACT

A method and apparatus for testing the glare susceptibility of a subject. The technique includes presentation of a glare source and a target to the subject&#39;&#39;s view and then varying the relative intensity of light emitted by the glare source and target to determine the subject&#39;&#39;s susceptibility to glare. In each of the testing devices disclosed herein, means are provided for varying the target image to present a different, indentifiable target to the subject. The relative intensity of glare in relation to the intensity of the target illumination may be controlled by varying the intensity of the target while maintaining the glare intensity constant, varying the glare intensity while maintaining the intensity of the target or a combination of both.

United States Patent 15 3,684,355 Molner [451 Aug. 15, 1972 [54] GLARESUSCEPTIBILITY TESTER OTHER PUBLICATIONS [72] Inventor: Stanley F.Molner, Cambridge, J. Blanchard, The Brightness Sensibility of the Mass.Retina," The Physical Review, 2ndSeries, Vol. Xl, No.2, February 1918,pps. 81- 99 [73] Assgnee' nmmetr'cs cambndge Mass" L. Holladay, TheFundamentals of Glare & Visibili- [22] Filed: July 2, 1970v ty," JOSA &Review of Scientific Instruments, Vol.

12, No. 4, April 1926, pps. 271- 319 [21] Appl 51826 M. Luckiesh et al.,A Visual Thresholdometer, Related U.S. Application Data 24, November[63] Continuation-in-part of Ser. No. 805,541, Primary Examiner-John K.Corbin March 10, 1969, abandoned. I Assistant Examiner-Paul A. Sacher IAttorney-Wolf, Greenfield and Sacks [52] US. Cl. ..351/36, 351/1,351/30,

351/39 ABSTRACT [51] Int. Cl. ..A6lb 3/06 A method and apparatus ftesting the glare suscepti- [58] Field of Search ..35l/l, 30, 36, 39bility f a Subject The technique includes presenter tion of a glaresource and a target to the subjects view [56] References C t and thenvarying the relative intensity of light emitted by the glare source andtarget to determine the sub- UNITED STATES PATENTS jects susceptibilityto glare. In each of the testing 1,437,809 12/1922 Jones ..351/1 xdevices disclosed herein, means are Provided for y- 2 209,728 7/1940l-ligley ..35 l/36 x ing the target image to p a different "Identifia-2,234 240 M1941 Frohring et a1 35 V36 ble target to the subject. Therelative intensity of glare 334l275 9/1967 Haugen 351/36 X in relationto the intensity of the target illumination 3355237 11/1967 Sim "2551/36X may be controlled by varying the intensity of the tar- 34l5594 12/1968A g m 1351/30 get while maintaining the glare intensity constant,34245l9 1969 1. 0 Ill X varying the glare intensity while maintainingthe inten- I lte sity of the target or a combination of both. 3,425,772v 2/1969 Mmas ..35l/39 3,436,146 4/1969 Minas ..35 l/l 9 Claims, 5Drawing Figures DRIVE CONTROL 4 4% MOTOR CIRCUITS fso PAIENTEmus 15 1912SHEET 1 0F 4 FIG. I

FIG. 3

INVENTOR.

STANLEY F. MOLNER BY flh gfizmw ATTORNEYS PATENTEDAum 1912 I 3.684.355

- SHE 2 UF 4 DRIVE CONTROL 4% MOTOR cmcuns fso FIG. 2

INVENTOR. STANLEY F. MO LNER ATTORNEYS PATENTED 15 3.684, 355

' saw u 0F 4 GLARE SUSCEPTIBILITY BACKGROUND OF THE INVENTION This is acontinuation in part of US. Patent Application Ser. No. 805,541, filedMar. 10, 1969, now abandoned.

This invention relates to techniques for measuring a subjects glaresensitivity. Interest in glare sensitivity as a diagnostic for visualand neurological problems, as a measure of the quality of fit of contactlenses, and as a requirement for automobile driver licensing tests isused with increasing frequency and the principal object of thisinvention is to provide a method and apparatus adapted to permit apersons sensitivity and susceptibility to glare to be reliablydetermined.

At the present time, ophthalmologists and optometrists determinesensitivity to glare subjectively. The doctor typically makes hisdetermination by shining a small flashlight in the patients eye andmaking a skilled judgement as to whether the patient is more or lesssensitive to glare than most other people he has tested. It is among theprimary objects of the invention to provide a method and apparatus fortesting a subjects glare susceptibility which does not require that thetest be administered by a trained, skilled ophthalmologist. Thetechnique may be employed by less skilled persons such as optometrists,technicians, medical assistants or others who have been trained tooperate the relatively simple testing device.

SUMMARY OF THE INVENTION To accomplish the objects of the invention, theglare susceptibility tester performs its function by making measurementof the loss of visualacuity under conditions in which the degree ofglare can be sensitively and repeatably varied.

In one embodiment of the invention, a constant color-temperature lightsource is provided and serves as the glare source. The intensity of theglare source is adjustable from zero to essentially full intensity. Thelight source shines into the eyes of the subject while a series ofstandard targets are sequentially presented to the subjects view. Thetargets are presented in a sequence of difierent attitudes ororientations and he is asked to identify the change in orientation ofthe target under variable glare conditions.

In another embodiment of the invention, the glare source is maintainedat a constant intensity throughout the test. The targets, however, arepresented to the subject under varying degrees of illumination and he isrequested to identify the changing target as the intensity of itsillumination changes in relation to the fixed intensity of the glaresource.

It is among the primary objects of the invention to provide an improved,simplified, technique for testing the glare susceptibility of a subject.

A further object of the invention is to provide a technique for testingthe glare susceptibility of a subject which does not require the skilledsubjected judgement of an ophthalmologist or other highly trained personand which also provides a standardized measure of glare susceptibility.

A further object of the invention is to provide a method and apparatusfor testing a subjects glare susceptibility which is suitable for useparticularly in mass testings of large numbers of subjects.

DESCRIPTION OF THE DRAWINGS These and other objects and features of thisinven tion along with its incident advantages will be better understoodand appreciated from the following detailed description of the preferredembodiments thereof, selected for purposes of illustration and shown inthe accompanying drawings, in which:

FIG. 1 is a perspective view showing a glare sensitivity'testerconstructed in accordance with this invention;

FIG. 2 is a diagrammatic illustration showing the interior of the testerof FIG. 1 and its mode of operation;

FIG. 3 is a perspective view of the target cassette used in the testerof FIG. 1;

FIG. 4 is a perspective view of another embodiment of the testing devicepartly broken away; and

FIG. 5 is a side elevation, partly in section of the device shownin-FIG. 4 as seen along the line 5-5 of FIG. 4.'

DESCRIPTION OF THE PREFERRED EMBODIMENT The glare testing device of thisinvention is embodied in a housing 10 having a front panel 12 providedwith a glare source opening 14 and a target opening 16. The tester alsoincludes a remote control box 18 connected to the main housing 10 bycord 20. In FIG. 1, the target opening 16 is shown formed in a plate 22that forms the front wall of a removable target cassette 24 shownseparately in FIG. 3, held in place by a pair of fasteners 26. Withinthe housing 10 are generally three systems, namely, glare source 28,target presentation section 30, and control section 32.

The glare source 28 includes a lamp 34 that may take the form of astandard incandescent projection lamp or some other form which producesa sufficient quantity of light. A condensor 36 mounted in the housingbetween the lamp 34 and the glare source opening 14 directs light fromthe lamp through the opening and to the subjects eye, represented at 38in FIG. 2. A variable density filter 40 in the form of a film loopinterrupts the light between condensor 36 and opening 14. The variabledensity film is used to vary the intensity of the glare directed at thesubject.

The film strip 40 is provided with approximately twenty discreet densityareas 40a from essentially opaque to essentially clear, so that theintensity of the glare may be changed from zero to effectively fulllight source intensity. Merely by moving the film strip so that thediscreet areas are sequentially placed between the condensor and theopening 14 the glare directed at the subject may be varied.

The target presentation section 30 includes a second film strip 42 whichcarries a number of standard targets 44 in random order. The targetstypically may be Landolt Rings, Es" etc. which the subject is asked toidentify as the test is conducted. In this embodiment, a light pipe 46may be employed to conduct light from the lamp 34 to illuminate thebackground for the target film 42 so that the targets may be viewedthrough the opening 16 as each is brought into alignment with theopening. Preferably the target film strip 42 is packaged in a cassetteas suggested in FIG. 3 which may carry the film in a loop or on reels sothat it may be advanced step by step by the target opening 16. Thecassette arrangement allows for a fast and simple interchange of thetypes and sizes of targets to suit the particular subject. In the formshown, the cassette may be quickly removed and replaced by means of thefasteners 26. The cassette in FIG. 3 is shown to carry a targetbackground filter 43 which determines the color and/or intensity of thebackground of the target viewed through the opening 16. Thus, glaresusceptibility with variations in color also may be tested by usingfilters of different color in the cassette.

The drive control 32 suggested schematically in FIG. 2 includes a drivemotor 48 carrying a shaft 50 which in turn bears sprocket assembly 52for moving the variable density strip 40 of the glare source 28. The endof the shaft 50 is connected by means of a one-way clutch 54 to a secondshaft 56, which carries a second drive sprocket assembly 58 for movingthe target strip 42 of the target presentation section 30. A controlcircuit is represented by box 60, which circuit includes the control l8and cable 20. The sprocket assembly may project through an opening inthe cassette 24 to engage the target strip if in fact the strip iscontained in such a cassette, or alternatively, the shaft 56 may engagethe sprocket assembly 58 which itself is contained within the cassette.

in the foregoing embodiment, with each forward actuation of the switch62 on control box 18, both the strips 40 and 42 advance one step, andthe indicator 63 on the box 18 identifies the particular frame of thestrip 40 intercepting the light from lamp 34. When the actuation of theswitch 62 is the forward direction, the strip 40 moves so as to increasethe intensity of the glare one step. When the examiner actuates theswitch 62 in the reverse direction, the one-way clutch 54 prevents thestrip 42 from moving so as to leave the target unchanged, but the glareintensity is reduced. This arrangement allows the examiner to graduallyreduce the brightness of. the glare source until the subject canidentify the orientation of the particular target exposed through theviewing opening 16. In a second operating mode, forward steps decreasethe glare intensity, and the examiner runs the device forward until thesubject is able to correctly identify the target orientation.Thereafter, the examiner retests the end point by reversing one or twosteps, requiring the subject to determine the target orientation again.In use, the examiner normally stands beside the subject and the cableallows him to assume this position and operate the glare testerremotely. By standing beside the subject but out of range of the glaresource, the examiner can identify the target in the viewing opening 16and at the same time, he can advance or reverse the variable densityfilter strip.

While in the foregoing embodiment, the variable tar gets are carried onseparate frames on the film strip within the cassette, it will beapparent that the variable target may be created by a fixed film with asingle image, and the size of the target may be changed by a lens systembetween the film and subject. Moreover, the color and/or intensity ofthe background may be changed by placing suitable filters between thefilm and subject.

it will also be appreciated that the glare source opening and the targetopening can be the same opening. in this embodiment, the target filmstrip is disposed between the variable density strip and the subject. In

this arrangement, there is only one fixation area to which to direct thesubject s attention.

FIGS. 4 and 5 show another embodiment of the invention in which theglare source and target are disposed in the same region with the glaresource preferably surrounding the target. This embodiment of theinvention includes a housing having a circular opening 72 formed in itsfront face 74. The subject faces the front face 74 of the device so thathe may direct his view through the opening 72. The image which ispresented to the subject through the opening 72 includes a centralidentifiable target and a surrounding glare ring 76. As described below,the relative intensity of the glare ring and the target illumination arevaried in a controlled manner to test the subjects glare susceptibilityunder varying conditions.

In this embodiment of the invention, the device includes a target wheel78 and a filter wheel 80 which are rotatable through the optical axis 83of the device about a fixed axis 82.

The target wheel 78 carries a plurality of circumferentially spacedtargets 84 mounted on transparent film or plate. As the target wheel isrotatably indexed, the targets 84 are presented to the optical axiswhich also passes centrally through the glare ring 76. The filter wheel80 includes a plurality of circumferentially spaced neutral densityfilters 88 of different densities which may be rotated into thealignment with the optical axis to vary the degree of illumination ofthe target. Illumination is provided by an appropriate incandescent bulb90 supported rearwardly within the housing 70 along the optical axis 83.The filter and target wheels are supported by a bracket 92 which hasopenings 94 formed in at least those portions which are disposed alongthe optical axis 83. The openings permit the light to pass unobstructedalong the optical axis and through the opening 72 in the front face 74of the housing 70. The device also includes a collimating lens 96 alongthe optical axis 83 and behind the target wheel 78. As shown, thecollimating lens 96 may be mounted on a lens support 98 which may beformed integrally with or secured to the bracket 92.

The target image presented to the subject is framed by an annular glarering shield 100 which is supported within the housing between the glarering 76 and the target wheel 78. The shield 100 preferably is mounted tothe removable front panel 74. The shield 100 has a central opening 102in alignment with the optical axis 83 and also includes a forwardlyextending peripheral flange 104 which embraces the periphery of theglare ring 76. The forwardly facing surface of the shield 100 preferablyis painted or otherwise coated with a white light-diffusive surface toreflect a major portion of the light from the glare ring back toward thesubject. Thus, the image presented to the subject consists of a centraltarget 86, illuminated to an intensity dependent on the selection of thefilter 88 on the filter wheel 80, with the target being surrounded by aring of relatively intense light. As described more fully below, thefilter wheel and target wheel are rotated to various positions toconduct the tests.

The target and filter wheels 78, 80 are supported near the. ends of ashaft 106 which is supported, between its ends, at the upper end of thebracket 92 by bearings 108. The shaft 106 is driven continuously by themotor 110 which is supported on the bracket 92. The motor 110 isconnected to a drive gear 112 which is secured to the shaft 106 by aconventional set screw 1 14 engagable with a flat 1 16 on the shaft 106.

The target wheel 78 is secured to a hub member 1 18 which, in turn, isrotatably joumaled about the forward end of the shaft 106 by thecylindrical bearing 120. The hub 118 and target wheel 78 are retained onthe forward end of the shaft 106 by a hand nut 122 which screws onto theshaft 106. The hub 118 and target wheel 78 are biased rearwardly towardthe drive gear 112 by a compression spring 124 retained in place by thewasher 126. A friction pad 128 which may be formed from felt or otherappropriate material is disposed between the facing surfaces of thedrive gear 112 and hub 118. In the absence of any force tending torestrain rotation of the target wheel, the target wheel 78 will rotatein unison with the shaft 106 and drive gear 1 12.

The foregoing drive arrangement for the target wheel 78 defines a slipclutch which is employed to index the target wheel to position aselected target 86 along the optical axis 83. Indexing is accomplishedby providing a plurality of circumferentially spaced holes 130 at therearward face of the hub 118 for engagement with a spring biased detent132. The detent 132 is mounted on a leaf spring 134, also is supportedon the bracket 92 which biases the detent 132 forwardly toward the holes130 in the hub 118. Thus, the detent 132 normally will be in engagementwith one of the holes 130 in the hub 118 to restrain motion of thetarget wheel 78 with the rotating shaft 106. The holes 130 arepositioned in relation to the targets 86 so that when the detent 132engages one of the holes 130, a corresponding target will be disposedalong the optical axis 83. In order to rotate and index the target wheelto present a new target to the subject, the detent 132 is withdrawnmomentarily to release the hub 118 which then is rotated by thefrictional engagement of the rotating friction pad 128. As soon as thenext hole 130 rotates into engagement with the detent 132, the targetwheel 78 is restrained with the corresponding target being exposed tothe subjects view. The detent 132 is retracted from engagement with thehub 118 by a target wheel solenoid 136 supported on the bracket 92 andhaving a retractable plunger 138 connected to the leaf spring 134. Thetarget wheel solenoid is operated by a conventional switch 140 which isaccessible externally of the housing 70.

The filter wheel 80 is mounted to the other, rearward end of the shaft106 by a similar slip clutch. This arrangement includes a hub 142 whichis secured about the rearward end of the shaft 106 by a set screw 144 inengagement with a flat on the shaft. The rearward face of the hub 142includes a circular felt pad 146 which bears against the facing surfaceof the filter wheel 80. The filter wheel 80 is rotatably mounted to therear end of the shaft 106 by a cylindrical bearing 148. The filter wheelis biased toward and into engagement with the felt pad 146 by acompression spring 150 which is retained in place together with thefilter wheel 80 by a nut 152 and washer 154 secured to the end of theshaft 106. Because of the engagement of the felt pad 146 with the filterwheel 80, the filter wheel will tend to rotate in unison with the shaft106 and the target wheel 78. Rotation of the filter wheel may beinterrupted, to

position a selected one of the neutral density filters 88 along theoptical axis of the device by a filter wheel solenoid 156 which operatessimilarly to the solenoid 136 associated with the target wheel 78. Thefilter wheel solenoid 156 also controls the retraction of a detent 158from the circumferentially spaced holes formed on the filter wheel 80.Operation of the filter wheel solenoid 156 and, therefore, indexing ofthe filter wheel is controlled by the switch which also controlsoperation of the target wheel solenoid 136 as described above.

The device is operated by a pair 'of simple control switches 140, 162which preferably are located at the side of the housing 70 to provideconvenient access for the operator. The switch 140, described above, isemployed to actuate either the filter solenoid individually or both thefilter and target solenoid 136, 156 simultaneously, depending on whichposition the switch is thrown to from the neutral position shown. Forexample, when the switch is pressed upwardly toward the positionindicated at F, only the filter wheel solenoid will be actuated topermit the filter wheel to rotate with the shaft until the switch isreleased to deactivate the solenoid and permit its detent 158 to enterthe next presented hole 160 in the filter wheel. This permits the targetto remain the same while varying the intensity of target illumination.When the switch 140 is depressed to the T-F position, both solenoids136, and 156 are actuated to cause both the target itself and the filterto change.

In the preferred embodiment. of the invention, the drive motor 110 is ofthe reversible type to enable the shaft and its associated wheels to berotated in either direction. This permits the filter wheel to be turnedto selectively increase or decrease the illumination of the target. Thedirection of rotation of the wheels 78, 80 is controlled by the switch162 which controls the polarity of the reversible motor 110. Forexample, when in the I position shown, the switch 162 will cause thefilter wheel 80 to be rotated in a direction tending to increase thetarget illumination. When in the opposite position D the direction ofrotation of the shaft 106 and filter wheel 80 is reversed to decreasethe target wheel illumination.

In order to monitor the target and target illumination intensitypresented to the subject, appropriate indicators are associated witheach of the wheels 78, 80. In the embodiment shown, this is achieved byforming flanges 164, 166 about the circumference of the target wheel 78and filter wheel 80 respectively. Appropriate markings corresponding tothe various target configurations and filter densities are spacedcircumferentially about the flanges 164, 166. Windows 168, 170 areformed in one of the walls of the housing to expose the calibratedflanges 164, 166 of the wheel 78, 80. The calibrations aredisposed onthe wheel so that when a given calibration is viewed through either ofthe windows 168, 170 the particular target or filter associated withthat calibration will be disposed along the optical axis 83 andpresented to the subject being tested.

A variety of testing techniques may be employed with the device to testthe subjects glare susceptibility. With the glare ring turned on, thefilter wheel 80 is rotated to present the least dense filter to theoptical axis thus illuminating the target to its maximum intensity. Thesubject is asked to indicate the target attitude, such as if the openingin the Landolt ring is facing up, down, right or left. The Examiner mayverify the sub jects response by observing the indicia in the targetindicator window 168. The examiner then momentarily depresses the switch140 to the T-F position to index both the target wheel and filter wheelone increment, thus presenting a different target illuminated at adecreased intensity. The subject then is again asked the attitude of thetarget. This procedure is continued until the glare of the glare ring isso intense in relation to the target illumination that the subject nolonger can perceive the target attitude. The examiner than notes theindicia appearing in the filter window thus providing a quantitativevalue of the subjects glare susceptibility. The examiner may then electto extinguish the glare ring and continue to reduce the backgroundillumination of the target until the subject can no longer perceive thetarget orientation. This second end point provides a measure of thesubjects visual acuity without glare.

Another testing technique may be employed to determine the subjectsglare recovery period. This technique includes progressively reducingthe target background illumination by incremental rotation of the filterwheel until the subject no longer can identify the target orientation.The glare source then is extinguished. The time lapse fromextinguishment of the glare source until the subject is able to identifythe target orientation is the glare recovery period.

When conducting tests, the unit preferably should be positioned so thatthe subject may look directly at the target while comfortably seated ata distance of approximately 10 feet. The room should be darkened or atleast dimmed as a brightly lit room makes reliable measurements somewhatdifficult. The subjects eyes may be tested simultaneously orindividually by employing a conventional occluder or eye patch.

if desired, the target wheel 78 may be changed. Different target wheelscorresponding to different degrees of visual acuity or different targetconfigurations or different forms of targets may be employed. In orderto remove or change the target wheel 78, the front panel preferably isremovable to provide access to the hand nut which is unscrewed simply topermit replacement of the target wheel.

Thus, 1 have described an improved method and apparatus for testingvarious visual perameters and, more particularly, that of a subjectsglare susceptibility. Moreover, the technique is suited particularly foruse by examiners who need not have had the skill and training necessaryto perform such tests according to previous techniques. it should beunderstood, however, that other modifications and embodiments of theinvention will be apparent to those skilled in the art without departingfrom its spirit.

Having thus described the invention, what is claimed l. A glaresusceptibility testing device comprising:

target means disposed within said device;

means for illuminating said target means;

a glare source comprising a generally annular light source disposed insaid device and being arranged to surround the image of said target aspresented to the subject;

means for varying the intensity of illumination of said target meanswhereby the relative intensity of said annular glare source and saidtarget may be controlled; and

means for shielding said target means from glare emittedby said glaresource.

2. A device as defined in claim 1 wherein said shielding meanscomprises:

a ring having a central opening formed therein, said opening beingadapted to permit the subject to view the target image framed withinsaid opening; said ring having an outer flange surrounding said annularglare source for reflecting light from said glare source away from saidtarget.

3. A device as defined in claim 1 wherein said means for varying thedegree of illumination of said target comprises:

a plurality of filters of different optical densities; and

means mounting said filters for sequential movement into the light pathdefined between said target and said illuminating means therefor. 4. Adevice as defined in claim 3 wherein said means adapting said target topresent said changing imagecomprises:

a plurality of different targets for sequential movement into theoptical path defined by said filtered illuminating light and in centralregistry with said annular glare source. V

5. A glare susceptibility testing device comprising:

target means disposed within said device;

means for illuminating said target means;

a glare source comprising a generally annular light source disposed insaid device and being arranged to surround the image of said target aspresented to the subject;

means for varying the intensity of illumination of said target meanswhereby the relative intensity of said annular glare source and saidtarget may be controlled;

means mounting said targets for movement and wherein said means mountingsaid targets for said movement further comprises;

a shaft rotatable the fixed axis;

said plurality of targets being mounted to a wheel in acircumferentially spaced arrangement;

said plurality of filters being mounted to another wheel incircumferentially spaced arrangement thereon;

means mounting said wheels to said shaft in spaced relation along saidshaft;

means for driving said shaft, said shaft and said wheels being arrangedto present selected filters and targets into alignment with the centralaxis of said glare ring; and

said means for illuminating said target comprising a light source on theside of said filter wheel which is remote from said target, said lightand said central axis of said glare ring defining the optical axis ofsaid device;

said drive means for driving said shaft being reversable whereby saidfilters and said targets may be presented in reversed sequence;

means mounting said filter wheel and said target wheel in said shaft forrelative and unitary rotary motion with said shaft; and

control means associated with said wheels for permitting or precludingsaid wheels to rotate in unison with said shaft.

6. A device as defined in claim further comprising:

said means for driving said shaft being reveisable to permit saidfilters and targets to be presented in a reversed sequence.

7. A device as defined in claim 5 wherein said control means forpermitting or precluding said filter wheelsto rotate in unison with saidshaft comprises:

detent means associated with each of said wheels,

said detent means being adapted to engage each of said wheels topreclude rotation of said wheels, said detent means being releasable topermit said rotation, said detent means being operable independently orin unison with each other.

8. A method of testing a subjects glare susceptibility comprising thesteps of:

presenting to the subject a target to be viewed;

presenting a glare source of a generally annular configurationsurrounding said target image as viewed by the subject;

maintaining said glare source at an intensity relative to that of saidtarget to prevent the subject from identifying the target; thereafterdiscreetly reducing the relative intensity of the glare to that of thetarget and simultaneously and incrementally changing the target imageuntil the target can be identified by the subject; and

shielding said target means from glare emitted by said glare source.

9. A method of testing a subject's glare susceptibility as defined inclaim 8 wherein said step of reducing the relative intensity of theglare to that of the target comprises maintaining the glare source at aconstant intensity and increasing the degree to which said target isilluminated.

=I i t

1. A glare susceptibility testing device comprising: target meansdisposed within said device; means for illuminating said target means; aglare source comprising a generally annular light source disposed insaid device and being arranged to surround the image of said target aspresented to the subject; means for varying the intensity ofillumination of said target means whereby the relative intensity of saidannular glare source and said target may be controlled; and means forshielding said target means from glare emitted by said glare source. 2.A device as defined in claim 1 wherein said shielding means comprises: aring having a central opening formed therein, said opening being adaptedto permit the subject to view the target image framed within saidopening; said ring having an outer flange surrounding said annular glaresource for reflecting light from said glare source away from saidtarget.
 3. A device as defined in claim 1 wherein said means for varyingthe degree of illumination of said target comprises: a plurality offilters of different optical densities; and means mounting said filtersfor sequential movement into the light path defined between said targetand said illuminating means therefor.
 4. A device as defined in claim 3wherein said means adapting said target to present said changing imagecomprises: a plurality of different targets for sequential movement intothe optical path defined by said filtered illuminating light and incentral registry with said annular glare source.
 5. A glaresusceptibility testing device comprising: target means disposed withinsaid device; means for illuminating said target means; a glare sourcecomprising a generally annular light source disposed in said device andbeing arranged to surround the image of said target as presented to thesubject; means for varying the intensity of illumination of said targetmeans whereby the relative intensity of said annular glare source andsaid target may be controlled; means mounting said targets for movementand wherein said means mounting said targets for said movement furthercomprises; a shaft rotatable the fixed axis; said plurality of targetsbeing mounted to a wheel in a circumferentially spaced arrangement; saidplurality of filters being mounted to another wheel in circumferentiallyspaced arrangement thereon; means mounting said wheels to said shaft inspaced relation along said shaft; means for driving said shaft, saidshaft and said wheels being arranged to present selected filters andtargets into alignment with the central axis of said glare ring; andsaid means for illuminating said target comprising a light sOurce on theside of said filter wheel which is remote from said target, said lightand said central axis of said glare ring defining the optical axis ofsaid device; said drive means for driving said shaft being reversablewhereby said filters and said targets may be presented in reversedsequence; means mounting said filter wheel and said target wheel in saidshaft for relative and unitary rotary motion with said shaft; andcontrol means associated with said wheels for permitting or precludingsaid wheels to rotate in unison with said shaft.
 6. A device as definedin claim 5 further comprising: said means for driving said shaft beingreversable to permit said filters and targets to be presented in areversed sequence.
 7. A device as defined in claim 5 wherein saidcontrol means for permitting or precluding said filter wheels to rotatein unison with said shaft comprises: detent means associated with eachof said wheels, said detent means being adapted to engage each of saidwheels to preclude rotation of said wheels, said detent means beingreleasable to permit said rotation, said detent means being operableindependently or in unison with each other.
 8. A method of testing asubject''s glare susceptibility comprising the steps of: presenting tothe subject a target to be viewed; presenting a glare source of agenerally annular configuration surrounding said target image as viewedby the subject; maintaining said glare source at an intensity relativeto that of said target to prevent the subject from identifying thetarget; thereafter discreetly reducing the relative intensity of theglare to that of the target and simultaneously and incrementallychanging the target image until the target can be identified by thesubject; and shielding said target means from glare emitted by saidglare source.
 9. A method of testing a subject''s glare susceptibilityas defined in claim 8 wherein said step of reducing the relativeintensity of the glare to that of the target comprises maintaining theglare source at a constant intensity and increasing the degree to whichsaid target is illuminated.